Adeno-associated virus (AAV) is a non-pathogenic parvovirus that requires the presence of a helper virus for a fully permissive infection. AAV has garnered much attention as a potential gene therapy vector. Although rapid strides are being made in vector development and clinical applications, the current lack of knowledge about several aspects of AAV biology limits this progress. For example, we only have a rudimentary understanding of how AAV replication (Rep) proteins regulate site-specific integration, replication, gene expression, and viral production. The Rep proteins also play a role in the interactions between AAV, its most efficient helper virus adenovirus (Ad), and the host cell. Most notable is the inhibition of Ad production by AAV during a co-infection. However, the mechanisms of this inhibition remain largely unknown. The proposed studies will test the overall hypothesis that AAV and its Rep proteins inhibit Ad production at the level of transcription and DNA replication. [unreadable] [unreadable]